Comment by Jan Paul (JIRA)

The problem doesnt' exist when I build the main.swift manually via swiftc -g main.swift just in case there was doubt 😉

This looks like a problem with the compiler or lldb. lldb doesn't work when we use create executable via objects:

$ cat main.swift
let str = "Hello world"
print(str)

This works:
$ swiftc -g -o sample -emit-executable main.swift
$ lldb sample
(lldb) b main.swift:2
(lldb) r
(lldb) po str
"Hello world"

This doesn't:
$ swiftc -module-name sample -g -emit-object -c main.swift
$ swiftc -g -o sample -emit-executable main.o
$ lldb sample
(lldb) b main.swift:2
(lldb) r
(lldb) po str
error: in auto-import:
failed to get module 'sample' from AST context

--
$ swift --version
Swift version 3.0-dev (LLVM 8226908317, Clang e82f59cafd, Swift ce722fe0a5)
Target: x86_64-unknown-linux-gnu
$ lldb --version
lldb version 4.0.0 (git@github.com:apple/swift-lldb.git revision 85e9e3cafb8cd2c58e1197510f48ac13e92fbde3 clang revision e82f59cafd6c10e2063bc46b53f99b96d397371b llvm revision 822690831754af558dabf4048dd7da5ed2ff2f00)

Toolchain: swift-DEVELOPMENT-SNAPSHOT-2016-11-15-a-ubuntu16.04

That's correct. Swift needs to include the swiftmodule in the debug info, so if you link in a separate step it doesn't have a chance to do that. Take a look at what swiftc -### does.

Comment by Jin Mingling (JIRA)

this seem more critical because the SPM debug outcome can not be debugged.

do we have some workaround, such as some flag to let lldb(swift version) load swiftmodule info by manual?

@belkadan Thanks, looks like if you pass swiftmodule in link step (with module name) it debugs properly.
#856

This is fixed right?

Nope, see PR

#933

The problem is package manager need to link main swiftmodule with the executable to make them debuggable. The PR #933 on package manager is currently blocked by SR-3863 (duped by SR-2660).

It looks like the debugging works fine without linking swiftmodule if there is a search path to the system module package. So if you invoke swiftpm with it, debugging will work:
$ swift build -Xcc -I/path/to/system/module

or if you convert the system module to a "fake" Clang module, swiftpm will automatically add a search path. This is of course not the correct solution but maybe is useful in the mean time.

@aciidb0mb3r/@neonichu any updates on this? Apparently this is blocking all debugging on Linux and also partially on macOS.

see https://bugs.swift.org/browse/SR-11543 🙁

I believe this is fixed in Swift 5.3. Comments in SR-11543 also suggest that this is fixed.